E. M. Doidge 15 



very hot and dry. A young culture was used, a number of young 

 leaves being inoculated on the 13th October by means of needle pricks, 

 and the tree covered over with a wet tent for 24 hours after inoculation. 

 This resulted in a number of small infections chiefly in the region of 

 the needle pricks. 



8. A second young tree was inoculated on the 3rd of November. 

 There were a number of very young leaves on the tree, which had not 

 yet lost their red colour ; in some of these minute punctures were made 

 with a fine needle and the whole was sprayed with the suspension of a 

 young culture in distilled water. The tree was covered with wet sacks 

 for 48 hours after inoculation. After 27—28 days, there were a few 

 infections on all the younger leaves of the tree, especially in the neigh- 

 bourhood of the needle pricks and a pure culture of the specific organism 

 was readily obtained from the infected areas. 



In both the above experiments the controls were entirely free from 

 disease. 



9. Attempts were made in the season 1911 — 12 to infect some fruits 

 of the "Maroola tree" (Sderocarya cajfra) but without success. 



Natural methods of infection. 



It has been noticed in every instance up to the present that the 

 spread of infection is in the direction of the prevailing winds. It seems 

 probable, therefore, that the wind is the principal agent in spreading 

 the disease and that the organism is carried to a large extent with the 

 dust from beneath the trees. It has been noticed that where the ground 

 is kept free of decaying vegetation and soaked with some germicide, 

 that the spread of infection is to some extent arrested. It has also been 

 observed that when the trees are growing among long grass the infection 

 does not spread nearly so rapidly as when the ground under the trees 

 is bare. This supports the supposition that the infective bacteria are 

 largely carried by the wind. 



The younger leaves and the fruit are undoubtedly infected by the 

 rain dripping from diseased leaves. An infected spot is almost invariably 

 found where two fruits are in contact and where a drop of water can 

 easily lodge. 



I have noticed very few insects on the trees; they do not appear 

 to feed to any great extent on the mango foliage, and one rarely sees 

 any leaves disfigured by insects. The common stink-bug (Anoplocnemis 

 curvipes) is sometimes found on the young foliage, but is probably not 

 responsible to any great extent for spreading the disease. 



